1. Field of the Invention
This invention relates to electrode structures that have good, reliable, robust contact to insulator materials having high dielectric constants, and, in particular, to forming capacitors in microelectronic devices with these electrode structures and high dielectric constant materials.
2. Description of the Related Art
Capacitors are critical devices in integrated circuit designs, particularly for high density memory chips such as dynamic random access memories (DRAMs).
Capacitance is proportional to both the electrode area in contact with the dielectric and the dielectric constant of the insulating material. As the trend toward increasing the number of devices on a single chip has made it necessary to make devices smaller and smaller, the way in which capacitors are fabricated has had to change. The problem of how to increase electrode contact area without using a lot of surface area on the chip has been addressed by changing the topography of capacitors. Former “flat sandwich” configurations, wherein the device consists of planar layers, one on top of another, have given way to “container” and “stud” configurations, among others.
A container capacitor is made inside a hole or via in a layer of insulating material. The layered structure forming the capacitor conforms to the shape of the via as the layers are deposited one on top of another. Thus, the electrode contact area includes both the cylindrical side surface of the container and the circular bottom. In some designs, the outside cylindrical surface can also be made available. Yet the capacitor uses a chip surface area (“footprint”) that is only the size of the circular top opening of the via.
Similarly, capacitors can be made in a stud configuration, wherein a column of electrode material is made through a series of deposition, photolithography and etch steps, and additional capacitor layers are deposited over the column, conforming to its outer surface. Again, the surface area of the chip occupied by the capacitor is small compared to the total electrode/dielectric contact area, or effective capacitor surface area, which includes the cylindrical side surface of the column, as well as the top portion.
Another way to get more capacitance out of a small area is to use dielectric materials with high dielectric constants (k), so-called HDCs, such as barium strontium titanate (BST) or tantalum oxide (Ta2O5). A difficulty with these materials is that they tend to lose oxygen during high-temperature processing, which causes undesirable changes in their dielectric properties and may oxidize nearby materials. Additionally, most processes for forming these materials involve highly oxidizing environments that can corrode conductive elements of the integrated circuit, such as underlying polysilicon plugs.
Accordingly, there is a need for processes and materials for formation of capacitors in integrated circuits, which are compatible with use of high dielectric materials. It would be advantageous to use a material that is a barrier to oxygen diffusion from these HDC's and also has the electrical conductivity characteristics necessary for a capacitor electrode.